The CW-21 was an all metal, low wing stressed skin aircraft with a semi-monocoque construction. Undercarriage was stowed upwards into clamshell fairings underneath the wings. Armament was twin 7.62mm machine-guns in the engine fairing, synchronised to fire through the propellor arc.
One 1938 prototype (c/n 21-1/NX19431).
There were three production models produced.
- NX19441 (c/n 21-2)
- NX19442 (c/n 21-3)
- NX19443 (c/n 21-4)
In addition, 27 disassembled airframes were shipped to China to be assembled for use there. These can be identified by the P-35 type wheel fairings instead of the clamshell type of the other Model 21.
24 21B built for the Netherlands. Sent to the Netherlands East Indies Air Force (NEIAF) when Netherlands was annexed by Germany. These models are identifiable by the inwards rotating, fairing-less undercarriage. Construction numbers 2853–2872, NEIAF classifications CW-344 to CW-363.
Total stated production of 62 unites between Models 21 and 21B.
This model featured a twin bladed propeller mated with a 450hp engine to fulfil a contract with the NEIAF. 36 built. 
The CW-21 rose out of a pre-war design at Curtis-Wright based on their own lightweight Model 19 twin seat utility aircraft. This was an air plane based on large sacrifices. In order to provide a rapid (for the time) rate of climb, speed and manoeuvrability, there was no armour or self sealing fuel tanks and armament was limited to two machine-guns.
Prototype and the first three production models all lost in crashes. All 27 airframes were lost when the Japanese advance destroyed the facility that was assembling them.
24 ordered by Netherlands, routed to NEIAF instead. These did not fare well against superior Japanese planes. Lack or armament,armour and fuel tank protection saw them outclassed and a number were lost on landing due to vision difficulties, aminly caused by the very long nose blocking forwards view.